Semiconductor memories include volatile memories such as DRAM (Dynamic Random Access Memory) and non-volatile memories such as flash memories. While known non-volatile memories include NAND flash memories and the like, ReRAM (Resistance Random Access Memory) is drawing attention as a device which is capable of being more miniaturized.
ReRAM uses a variable resistor, which changes resistance in response to changes in the electric voltage, as a resistance element. A typical type of this variable resistor has at least two layers of metal oxide layers which are different in the degree of oxidation or the resistivity, and has a structure in which these layers are sandwiched between top and bottom electrodes. For example, in the following Patent Document 1, there is described a resistance element that has a bottom electrode (Pt), and a titanium oxide film, a nickel oxide film and a top electrode (Pt) laminated thereon in the order.
Patent Document 1: International Publication No. WO 2008/107941